FE: Add Cypress tests for mobile header and footer; audit existing unit tests for both

[randimays]

Description

In #15414, we added Cypress tests for the desktop header and footer in vets-website. We need to add Cypress tests for the mobile header and footer as well as audit the existing unit tests for both (clean them up, add/remove where necessary).

User story

Describe the audience/user, enhancement or fix, and value / outcome desired.

AS A Product Owner
I WANT adequate test coverage of my products
SO THAT I know Veterans see consistent behavior.

Engineering notes / background

We may be able to reuse tests/ code from the desktop header / footer, with minimal modifications.
Megamenu naming / testing needs to be reviewed / stay consistent.

Acceptance criteria

• Audited existing mobile header/footer coverage
• Added tests to cover any gaps
• All tests pass consistently

[randimays]

I have completed all the Cypress tests for mobile on the header. Need to add mobile tests for the footer and complete the audit of unit tests (part of this is finished already).

[randimays]

Adding a lengthy Slack thread regarding header/footer test brittleness (due to checking data coming from the CMS). I'll make adjustments in this ticket based on the proposed solutions at the bottom of the thread.

[randimays]

• Merged a PR that reduces content-build Cypress tests to a simple-ish smoke test. Since CB relies heavily on Drupal data to build the homepage, I only tested the basics.
• Two PRs for the vets-website changes (neither are merged yet, working on CI and approvals)
  • This one is a cleanup PR for removing unnecessary comments and updating imports in the header/footer code
  • This one finalizes Cypress and unit tests for the header and footer in vets-website, removing Drupal-dependent tests and using mock data instead.

[randimays]

All PRs referenced above have been merged in. Closing!